FIGS. 1a to 1n are schematic flow diagrams showing the process for manufacturing a conventional light-emitting diode. Conventionally, in the fabrication of the light-emitting diode, a substrate 100 is firstly provided, in which the substrate 100 is a sapphire substrate, for example. Next, an N-type cladding layer 102, an active layer 104 for illuminating and a P-type cladding layer 106 are grown on the substrate 100 in sequence by an epitaxial method, in which a material of the N-type cladding layer 102 is N-type doped GaN, and a material of the P-type cladding layer 106 is P-type doped GaN. Then, a contact layer 108 is formed on the P-type cladding layer 106, such as shown in FIG. 1a. A material of the contact layer 108 is P-type doped GaN.
A nickel metal layer 110, which is used as an etching mask layer, is deposited to cover the contact layer 108. A photoresist layer 112 is coated on the nickel metal layer 110 to form a structure such as shown in FIG. 1b. After the photoresist layer 112 is formed, a pattern is defined into the photoresist layer 112 by a photolithography process and a first mask (not shown), in which a portion of the photoresist layer 112 is removed to expose a portion of the nickel metal layer 110, such as shown in FIG. 1c. The exposed portion of the nickel metal layer 110 is etched and removed by using the patterned photoresist layer 112 as an etching mask until the underlying contact layer 108 is exposed, so that the pattern in the photoresist layer 112 is transformed into the nickel metal layer 110, such as shown in FIG. 1d. After the pattern is transformed into the nickel metal layer 110, the remaining photoresist layer 112 can be stripped, so that a structure such as shown in FIG. 1e is formed.
Next, the exposed portion of the contact layer 108 as well as the underlying portions of the P-type cladding layer 106 and the active layer 104 are etched and removed by using the patterned nickel metal layer 110 as an etching mask until the N-type cladding layer 102 is exposed, such as shown in FIG. 1f. The remaining nickel metal layer 110 is removed to expose the contact layer 108, such as shown in FIG. 1g. After the nickel metal layer 110 is removed, a transparent contact layer 114 is deposited on the contact layer by using a second mask (not shown), in which the transparent contact layer 114 is composed of a Ni/Au structure. For better process reliability, the edge of the transparent contact layer 114 and the edge of the contact layer 108 are separated by a distance, i.e., the transparent contact layer 114 is just located on a portion of the top surface of the contact layer 108 rather than the entire top surface of the contact layer 108, such as shown in FIG. 1h. After the transparent contact layer 114 is formed, a thermal alloying treatment is performed on the transparent contact layer 114 to form ohmic contact between the transparent contact layer 114 and the contact layer 108, such as shown in FIG. 1i. 
After the thermal alloying treatment of the transparent contact layer 114 is completed, a cathode contact layer 116 is deposited on a portion of the exposed portion of the N-type cladding layer 102 by using a third mask (not shown), so as to form a structure such as shown in FIG. 1j. The cathode contact layer 116 is composed of a Ti/Al structure. Then, a thermal alloying treatment is performed on the cathode contact layer 116 to form ohmic contact between the cathode contact layer 116 and the N-type cladding layer 102, such as shown in FIG. 1k. Next, a cathode electrode 118 and an anode electrode 120 are respectively deposited on the cathode contact layer 116 and a portion of the transparent contact layer 114 by using a fourth mask, such as shown in FIG. 11. Each of the cathode electrode 118 and the anode electrode 120 is composed of a Ti/Au structure.
After the cathode electrode 118 and the anode electrode 120 are formed, a dielectric film, which is used as a protective layer 122, is deposited to cover the cathode electrode 118, the anode electrode 120, the exposed portion of the contact layer 108, the transparent contact layer 114, the N-type cladding layer 102, the cathode contact layer 116, the P-type cladding layer 106 and the active layer 104, such as shown in FIG. 1m. Subsequently, a definition step is performed on the protective layer 122 by using a fifth mask (not shown), to remove portions of the protective layer 122 located on the cathode electrode 118 and the anode electrode 120 and expose the cathode electrode 118 and the anode electrode 120, so that the fabrication of the light-emitting diode device such as shown in FIG. 1n is completed.
In the processing of the conventional light-emitting diode, because the nickel metal layer 110 is used as the etching mask, the contamination of metal material may occur to result in a short circuit in the device. In additional, due to the limitation of the process, the size of the transparent contact layer 114 is less than that of the contact layer 108, so the illuminating area of the device is decreased to reduce the brightness of the device. Furthermore, the transparency of the transparent contact layer 114 is lower, and a thermal alloying is additionally needed for a better ohmic contact while using the Ni/Au structure as the transparent contact layer 114, so that the brightness of the device is lowered and the amount of the process steps is increased to raise the cost. Moreover, in the entire process, five masks are needed, so that the cost is greatly increased, many extra process steps are added, the process time is prolonged to result in lowered productivity, and the product yield is adversely affected.